1. Field of the Invention
The present invention relates to rice-based food compositions and to their methods of preparation. More particularly, the present invention relates to high protein rice flour (HPRF) nutritionally complete formulas and most particularly to infant formula. In its methods aspect, the present invention relates to methods for preparing high protein rice flour suitable for use in rice-based infant and adult nutritional formulas.
2. Description of the Prior Art
Rice is a starchy food containing approximately 6-10% protein. Rice flour, as a raw material of nutritional value, constitutes an inexpensive by-product of rice milling obtained by grinding broken rice. Conventional milling practices produce rice flour composed largely of about 80% carbohydrate with about 7-9% protein material. However, the PER (protein efficiency ratio-ratio of weight gain of rats to protein consumed of a 10% protein diet) for rice is 2.18 which is almost equivalent to that of beef (2.30), a considerably more costly protein source. Because of the low concentration of protein in rice and the resulting bulk required to obtain a satisfactory protein intake, infants and children cannot eat a sufficient amount to meet their protein requirements.
Efforts to improve the protein quantity of rice involving selected breeding of new rice varieties have not met the protein content required by young children. Research directed to the production of rice flour with increased protein content has been conducted. Prior art within this general area includes the following papers.
Hansen, et al., Food Technology, 35 (No. 11), pages 38-42 (1981) developed a high protein rice flour (25% protein content) by using the enzyme alpha-amylase to digest the starch material of milled broken rice thereby decreasing starch content resulting in increased protein content compared to the original rice flour. In the Hansen, et al. process, a 5% slurry of finely ground crude rice flour is first heated for 30 min. at 100.degree. C. to effect gelatinization, then partially digested by enzyme (alpha-amylase) treatment, centrifuged and the precipitated HPRF freeze-dried. Protein level of HPRF was reportedly increased three-fold over the starting material (approximately from about 8% to 25%). The supernatant is principally carbohydrate (98.3%).
Chen, et al., J. Sci. Food Agric. 35, 1128-1135 (1984) modified the Hansen et al. process to provide both HPRF and high-fructose rice syrup from broken rice. In the Chen, et al. process, a 20% slurry of the milled broken rice is mixed with calcium chloride (70 mg/kg rice), pH adjusted to 6.5 and digested (liquified) with alpha-amylase optimally at 90.degree. C. for 90 min.; specifically with Termamyl 60L alpha-amylase obtained from NOVO Industri, A/S, Denmark. The liquified mixture is centrifuged and the precipitated HPRF dried. Protein content of the HPRF was similar to Hansen, et al. (approximately three times as high as the raw material). The supernatant is saccharified at 60.degree. C. with glucoamylase and then isomerized to fructose with glucose isomerase to provide a high-fructose rice syrup containing 50% glucose, 42% fructose and 3% maltose.
Chang, et al., Journal of Food Science, 51 (No. 2), pages 464-467 (1986) further modified the Hansen, et al. process to produce a rice flour with increased protein and calcium contents. According to Chang, et al., processing conditions for the production of HPRF concerned treating gelatinized rice flour slurry with calcium chloride and alpha-amylase 60.degree. C. for 90 min. The hydrolyzed starch is removed by centrifugation and the precipitated paste freeze dried to yield high protein rice flour with approximately 38% protein, a PER ratio of 2.17 and an amino acid composition similar to the rice flour of Hansen, et al.
It is evident that the prior art mentioned above describes a fundamental process for preparation of high protein rice flour (HPRF) wherein rice flour is gelatinized and enzymatically digested with carbohydrate-type enzymes commonly known as amylases. This treatment hydrolysis the starch to soluble saccharides of various molecular weights such as glucose, maltose, oligosaccharides, and dextrins from which the insoluble HPRF is separated, for example by centrifugation. Thus, by partial removal of the non-proteinaceous material, the processed rice flour contains less carbohydrate and the protein content is correspondingly enhanced.
High protein rice flour obtained as described in the prior art has not proved to be entirely satisfactory as a raw material for nutritional products. For instance, over 80% of rice protein consists of glutelin which is completely insoluble at pH's acceptable for infant formula. Infant formulas made with such protein do not form satisfactory dispersion, have a very grainy, gritty mouthfeel and tend to plug up the nipple. Moreover, the HPRF prior art process does not address the problem of unacceptable manganese levels. The manganese content of commercially available rice flour varies considerably with a typical content of about 150-260 micrograms (mcg) per gram protein. Table I below illustrates observed variations in manganese content of representative commercial rice flours containing about 8% protein.
TABLE I ______________________________________ Manganese Content of Commercial Rice Flours Source Manganese, mcg/g Protein ______________________________________ Riceland Foods.sup.a 150-163 California Rice Growers 150-200 Association.sup.b Riviana Rice Flour.sup.c 150-250 Coor's rice flour.sup.d 220-260 ______________________________________ .sup.a Stuttgart, AR .sup.b Sacramento, CA .sup.c Houston, Texas .sup.d ADM Milling, Rice Div., Weiner, AR
We have determined that using such rice flour as raw material in the conventional prior art process (gelatinization and enzymatic digestion) results in a concomitant enrichment of manganese along with increased protein content. Apparently, the manganese associates with the protein and remains with the separated HPRF rather than the solubilized saccharides.
Manganese is considered an essential element in the mammalian diet. It is also known that only relatively small quantities are required by human infants. Human milk levels are generally below 32 micrograms per quart and pediatric nutritionists favor infant formula with relatively low manganese levels. The National Academy of Sciences-Food and Nutrition Board (NAS-FNB) has determined the U.S. average daily intake and the estimated safe and adequate daily dietary intake as follows.
______________________________________ Dietary Intake U.S. Avg. Daily Intake Infants 10-300 mcg/day Children, 3-5 yrs. 1,400 mcg/day Children, 10-13 yrs. 2,180 mcg/day Adults 2,500-9000 mcg/day Estimated Safe and Adequate Daily Dietary Intake Infants 0-6 months 500-700 mcg/day Infants 6-12 months 700-1000 mcg/day Children and Adolescents 1,000-3,000 mcg/day Adults 2,500-5,000 mcg/day ______________________________________
A quart of infant formula typically contains about 14-20 g protein. As previously mentioned, the HPRF of the prior art retains substantially all of the manganese found in rice flour raw material which has typical manganese levels of 150-260 micrograms per gram protein. Thus, the amount of manganese in a quart of rice protein based infant formula containing 14 to 20 grams protein is calculated as follows for particular levels of rice flour manganese content.
______________________________________ CALCULATION 1 Manganese Per Quart Formula From Rice Flour (grams protein .times. mcg manganese per gram) Mn Content of Rice Micrograms Manganese per Quart Flour (mcg/g) Protein 14 g protein 20 g protein ______________________________________ 150 2100 3000 260 3640 5200 ______________________________________
With the assumption that an infant's diet includes one quart of formula per day, rice flour as a source of protein can contaim a maximum of about 50 mcg of manganese/g protein (estimated maximum safe and adequate daily dietary manganese intake of 700 mcg/day divided by 14 grams of protein). Since rice flours generally available contain considerably more than 50 mcg manganese/gram protein, they cannot be used to make HPRF suitable for infant formula.